Why Is the Ozone Hole Shrinking?

What caused the hole in the ozone layer? And how has science helped us begin to shrink the hole?

Sabrina Stierwalt, PhD,
January 3, 2017
Episode #220

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nasa.govTaking action to protect our planet can seem like a daunting or even futile task. Scientists have to navigate a complicated ecosystem with many interwoven variables in order to link an effect (like increased droughts or unusually intense storms, for example) with a cause. Politicians spanning many countries and cultural differences then have to come up with a plan, and entire industries have to agree to invest in that plan.

As we ring in the new year of 2017, let’s look at one of my favorite science stories from 2016: a story that tells us that all of that is possible. Science can save the world, with a little help, of course, from the cooperation and investment of its inhabitants.

What caused the hole in the ozone layer?

In 1985, a trio of British researchers noticed a hole in the ozone layer, our protection against harmful UV rays, over the Antarctic. Almost ten years earlier in 1974, scientists had noted a link between possible damage to the ozone layer and the release of chlorofluorocarbons in to the atmosphere, work which later earned those authors, Mario Molina and Sherwood Rowland, along with Paul Crutzen, the Nobel Prize in Chemistry.

In the 1970s and 1980s, chlorofluorocarbons or CFCs were readily used in coolants for refrigeration systems and everyday propellants like hair sprays or other aerosols. CFCs are fairly stable molecules so, once released, they almost always make their way up into the stratosphere, the layer of the Earth’s atmosphere that starts about 10-20 kilometers up (depending on where on Earth you’re located). They do not stay trapped inside the walls of your apartment, as has been incorrectly suggested by the US president elect.  

Once in the stratosphere, CFCs are more exposed to ultraviolet radiation which breaks them down into their constituent parts, including chlorine atoms. These chlorine atoms in turn react with oxygen atoms, a process which leads to the destruction of the molecules that make up the ozone. Less ozone means increased risk of skin cancer and cataracts for us Earthlings.

The 1987 Montreal Protocol

In 1987, only two years after the study noting the depletion was published in the journal Nature, a global agreement was reached with the intent of phasing out the use of so-called ozone depleting substances, including CFCs. This agreement, known as the Montreal Protocol, has been ratified by 197 parties, including the European Union and all of the United Nations members, and is one of the greatest success stories in global cooperation. Kofi Annan, the former Secretary General of the United Nations, called it “perhaps the single most successful international agreement to date.”

Production of CFCs was mostly stopped in the 1990s, but they can still be found in some old appliances and in a few countries. Meeting the goals of the agreement continues to require renewed investment. The Protocol has been amended four times and billions of dollars have been spent on helping lesser-developed countries as they continue to transition away from CFCs. The CFC molecules also live in the atmosphere for as long as 50-150 years, so the emissions you released in getting those perfect feathered bangs in the 1980s? They’re still up there.


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